There is currently a growing interest in the utilization of low temperature energy sources, especially low temperature liquid heat sources, for power production. Processes for generating power from low temperature liquid heat sources, such as geothermal brine, solar ponds, ocean thermal energy conversions (OTEC), waste heat, etc., are known.
In one such process, generally referred to as a direct flash process, the low temperature liquid heat source is flashed, i.e., vaporized. The vapor thus produced is passed to a power turbine or the like.
In the turbine the vapor is accelerated by a pressure drop. The accelerated vapor is directed against the blades of the turbine which results in the production of mechanical rotary motion which can be employed to generate electrical power. The vapor is then discharged from the turbine at a reduced pressure.
A modification of the direct flash process is referred to as a binary process, wherein heat from the low temperature liquid heat source is first transferred to a secondary working fluid, typically an organic mixture having a lower boiling point than water. The working fluid is then flashed to produce vapor. The vapor is passed to the power turbine to produce power.
In either process, the initial pressure of the vapor entering the turbine is relatively low as a result of the relatively low temperature of the liquid heat source. In order for the process to produce sufficient power to be practical, the pressure drop through the turbine requires that the pressure of the exhaust be near or below atmospheric pressure. Reducing the pressure of the exhaust below atmospheric pressure requires a closed system, including condensers for condensing the vapor in the exhaust.
Among the difficulties associated with the production of power from low temperature heat sources, is the inherently low theoretical thermodynamic efficiency associated with low temperature heat sources which results in low power outputs. It is thus important that the efficiency of all steps of such a process for producing power from low temperature heat sources be maximized.
Present processes utilize conventional condensers having metallic tube and shell arrangements. Such condensers are not only expensive, but provide relatively inefficient heat transfer.